In particular, the present invention relates to a splicing device of the aforementioned type comprising grip means designed to grip the sheet material to a given pressure and impart a given thrust on the edges for bringing them together, said grip means comprising pressure means and counterpressure plate means.
In connection with splicing devices of the aforementioned type, U.S. Pat. No. 4,454,000 relates to a manual splicing device wherein said pressure means, constituting one of the jaws of said grip means, comprise two disks (one of which is powered) inclined in relation to each other and contacting along the point of tangency facing said counterpressure plate means constituting the other jaw of said grip means. At said point of tangency, the two disks are connected so as to turn in the same direction about their respective axes, and are hinged to the counterpressure plate means so as to turn, in relation to and towards the same, by virtue of an adjustable thrust member. At said point of tangency, the outer edges of the two disks contact two externally threaded rollers inclined in relation to each other, mounted in idle manner on said counterpressure plate means, and connected so as to turn in the same direction.
In actual use, the operator inserts the front edge of the counterpressure plate means under the sheet material, so that the edges for splicing are located on opposite sides of a dividing rib on the plate means. The operator then moves the splicing device along the path defined by the two facing edges, which slide along the plate means and, at said point of tangency, between the inclined disks and inclined threaded rollers, which cooperate in such a manner as to bring together and pressure bond the edges.
The above noted splicing device has proven extremely effective in terms of performance, but definitely unsuitable for mass production use. In addition to requiring skilled labor, almost exclusively for operating the splicing device, it introduces into a substantially automatic production cycle an operation which cannot be predicted accurately in terms of performance time. This is mainly due to the critical nature of the first stage in the operation, wherein the counterpressure plate means are inserted under the sheet material which, being sticky and of relatively unstable shape, is easily crumpled.